Add a test_runner option

I tried to convert my tests to unittest2 (I need the skip decorators) and it worked when run by unittest2 but not really with setup test command; it's raised a warning (unittest2/case.py:317: DeprecationWarning: Use of a TestResult without an addSkip method is deprecated
self._addSkip(result, skip_why) and test shows as OK instead of SKIPED.